Since 1973, the rate of energy inflation has often exceeded the rate of general inflation. This fact increasingly affects the home-ownership ability of most individuals and families. There are no easy solutions to the "energy crunch". The supply of fossil fuels is diminishing. Nuclear plant construction and operation costs have increased greatly. Available biomass could be converted into concentrated fuels, but there is a low efficiency of conversion. New and economical technological solutions--photovoltaics, wind powered generators, ocean tidal generators, thermal systems, alternative fuels and other sources of energy--appear to be years in the future.
In view of the above, the uses and possible uses of solar energy are receiving more and more attention. The true potential of solar energy cannot be determined until many different factors are evaluated. These factors include such things as climatic conditions, outside temperatures, speed and direction of winds, topography, the amount of radiation, azimuth and altitude, shading, solar access, the sun's path, community acceptance, etc.
Assuming that a reasonable potential for solar heating and cooling are available, overall energy savings and the cost of achieving these savings can be determined as follows: First, evaluate the total heating requirements. Next determine what percentage of these requirements can be met by any particular solar collector with or without a complete storage system. Then analyze the overall cost of any proposed solar system considering actual energy savings, as well as dollar savings, when compared to conventional or alternative heating methods.
For example: The average daily winter space-heating requirements for a typical house in Raleigh, N.C., are about 2.32 therms or 23,200 BTU's (British Thermal Units) per day. At this same location, the average Jan. BTU's per square foot/day are 867 on a horizontal surface and 945 for a vertical surface. At the optimum space-heating-collection angle for Raleigh (approximately 45.degree.), an average of 1,282 BTU's sq. ft./day are available.
A good 60 square foot active solar collector will cost from five to six thousand dollars. Such an active unit will collect some 650 to 800 BTU's sq. ft./day. An efficient water or rock storage system--or "phase change" storage material--will cost an additional four to seven thousand dollars. If properly constructed, these systems can store 95% of the heat collected. Any of these systems have a daily potential of 45,600 BTU's (60 sq. ft. times 800 BTU's times 95%), or nearly two days' heating supply. When there are two or more consecutive winter days with cloud cover, space-heating will have to be provided by a back-up system. Given total cost of collectors, storage, and back-up heating, an active solar design does not appear to be cost-effective in terms of 1983 dollars.
If solar space-heating is to pay for itself in today's economy with its high interest rates, people have begun to think in terms of direct solar gain. Although many experimental structures have been built, adequate passive heat storage capacity as well as adequate insulating means to prevent heat loss during non-solar periods have plagued the industry and has made passive solar structures something less than completely desirable.